Penguin Tags Are a Drag -- Can Rubber Improve Them?

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Sue Jackson studies ecological and evolutionary physiology at the University of Stellenbosch in Matieland, South Africa. In 2002 she published a review paper on the impact of tags on penguins. She is concerned the new tags simply perpetuate a "bad system."

According to Jackson, any external tag attached to a flipper will cause some degree of hydrodynamic drag. And any degree of hydrodynamic drag is unacceptable, she said.

"Even if the band shape looks streamlined, it is not streamlined relative to the shape of the penguin, and that turns out to be very important for how much energy they use when they swim," she said.

Jackson said a 5 percent increase in the amount of energy it takes for a penguin to swim after and capture its prey is equivalent to a 5 percent rise in the cost of food at the grocery store.

Such an increase impacts how much food the penguin eats, how long it lives, and the survival of its offspring—the very type of demographic data the tags are designed to collect.

According to Boersma, all tags have a cost, but researchers "have to have some way to identify individuals if you are interested in demographics, or interested in differences in individuals over their lifetimes or age groups."

Alternative Identities

Barham acknowledges that some researchers "are totally opposed to external marking of birds." As an alternative, a member of his lab at Bristol University is developing computer software to identify African penguins by unique feather patterns on their chests.

The problem with such a system, according to Boersma, is the labor and time cost of taking a picture of an individual and then running the image through a database to search for a match. The system is also several years from being fully developed.

"There's no doubt we can learn individual penguins, but having 200,000 pairs in a colony makes it difficult," she said.

Jackson encourages the research community to more widely adopt an alternative: the use of so-called transponder tags that are implanted under the skin. Whenever the penguin walks past a receiver, the penguin's identity is revealed.

However, scientists say such a system is more expensive than the plastic or stainless steel tags. Also, transponder-tagged birds cannot be identified without a receiver, and the equipment requires considerable maintenance. The transponder tags also have high failure rates and can cause infections.

"They do, however, yield data that are not flawed by the substantial negative effects on the very parameters that flipper bands are used to study: annual adult and juvenile survival at sea, and breeding success," Jackson said.

According to Boersma, no tagging technique is ever going to be perfect for all situations and all species of penguins. Another question researchers need to be asking, she said, is, "When do you need to mark an individual and when don't you?"

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